A hang glider typically includes a sail or flexible membrane, a frame to support the sail, and a support attached to the frame. In use, the pilot holds the support and is able to soar through the air.
The majority of flexible wing hang gliders use a single surface, flexible membrane to provide an airfoil shape. The flexible membrane is attached to the frame by wrapping a portion of the flexible membrane around a frame member and stitching the flexible membrane to form a permanent attachment. In flight, air pressure forces the membrane into an airfoil shape. A hang glider of this type is shown, for example, in my U.S. Pat. No. 3,936,012.
While a hang glider of the above-described type works very satisfactorily, an improved airfoil can be obtained when upper and lower flexible membranes are used. One approach is to use the doped fabric construction which has been used for aircraft wings. One problem with the doped fabric construction is that the fabric becomes relatively rigid. A rigid fabric is not suited for hang glider usage in that the rigid fabric cannot be folded, and so it would be impossible to collapse the hang glider.